Muscle Mass - yes, important for so many bodily functions and especially important for us older individuals.
But it's also a primary consideration in human 'shock absorption' and preventing impact injuries.
Weight lifting does not 'build' muscle mass - weigh lifting creates the conditions which stress the body to induce muscle strengthening and building. As do other processes which induce muscle building.
To build muscle - the fundamental ingredients need to be available in the body... Proteins and enzymes needed for the building process.

I have had difficulty 'retaining' muscle these past few years, I'm about 15 lbs lighter than I'd like to be - as relates to a relatively 'lean' body with adequate muscle...
I have enough 'insulation', need more of the important tissue - good blood levels, muscle and well performing gray matter...
Besides natural sources for important body nutrition, I take Vitamins (assorted), Beta Alanine, HMB, and now Creatine.

For those who have not done much investigation, here's what Google AI has to say...
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"...Alternatives to creatine for boosting exercise performance, muscle growth, and energy metabolism include supplements that enhance muscle buffering capacity, support protein synthesis, or improve blood flow, such as beta-alanine, HMB, BCAAs, and beetroot juice. These options provide similar benefits for endurance and strength without the water retention often associated with creatine.
Top Alternatives to Creatine

• Beta-Alanine: Increases carnosine levels in muscles, reducing fatigue and improving endurance during high-intensity exercise.
• HMB (Beta-hydroxy-beta-methylbutyrate): Helps preserve muscle mass, particularly during intense training or dieting.
• Branched-Chain Amino Acids (BCAAs): Specifically leucine, isoleucine, and valine stimulate muscle protein synthesis and aid in recovery.
• Beetroot Juice/Powder: Provides nitrates that improve blood flow, enhance oxygen delivery, and improve energy efficiency.
• Betaine: May assist in improving power output and boosting cell hydration.
• Whey Protein: Supports muscle repair and growth, providing essential amino acids for recovery.

Natural Dietary Sources of Creatine
If a supplement alternative is not preferred, the body can acquire creatine directly from foods:

• Red Meat & Pork: Beef and pork are excellent, natural sources of creatine.
• Fish: Herring, salmon, and tuna.
• Other: Dairy products, such as milk and cheese, also provide small amounts.

Key Considerations

• Efficacy: While alternatives provide benefits, creatine monohydrate is often considered the most effective, safest, and cheapest option for strength.
• Combination: For optimal results, these supplements can be combined with a balanced diet and structured training program. "
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Aging creates more and newer challenges, especially if one still wishing to participate actively in living.
I know if I don;t pursue possibilities, nothing will 'improve'. Which means a 'decline' at this point in life.
Somethings work out, others need to be off the list. Reasonable efforts in 'trying' are an essential part, for me.
Ride On
Yuri

EDIT: I'm also taking WHey Protein, because my overall protein intake is well below 70 g /day. And given I'm riding (and infrequently doing other physical stuff) every day; I need to increase my protein intake some significant amount... I could increase in meals, but having a protein shake after my session seems a much easier and possibly a more timely process.